A fast spectrum nuclear fission reactor (“a fast neutron reactor”), such as a sodium fast reactor, generally includes a reactor vessel containing a nuclear reactor core. The nuclear reactor core includes an array of device locations for placement of fuel assembly devices and other reactor support and control devices. Fissile nuclear fuel within the nuclear reactor core is subjected to neutron collisions that result in fission reactions. In a breed-and-burn fast neutron reactor, a fission chain reaction yields “fast spectrum neutrons” that, in turn, collide with fertile nuclear fuel, thereby transmuting (“breeding”) the fertile nuclear fuel into fissile nuclear fuel. Liquid coolant flows through the nuclear reactor core, absorbing thermal energy from the nuclear fission reactions that occur in the nuclear reactor core. The heated coolant then passes to a heat exchanger and a steam generator, transferring the absorbed thermal energy to steam in order to drive a turbine that generates electricity. Design of such nuclear reactors involves combinations of materials, structures, and control systems to achieve desirable operational parameters, including nuclear reactor core stability, efficient thermal generation, long-term structural integrity, etc.